Seeding the Solar System with Life

by Paul Gilster on March 22, 2006

For years now, we’ve had our eye on Mars rocks that are known to occasionally fall to Earth, blown off their planet of origin in some primeval impact. But recent computer modeling suggests that a reverse process may also occur: rocks from Earth, potentially carrying life, could reach environments as distant as Europa and Titan.

The numbers are surprising. As presented by Brett Gladman (University of British Columbia, Vancouver) at the Lunar and Planetary Science Conference, from 30 to 100 objects from Earth would hit Europa after a period of 5 million years. Titan receives 20 hits. The question then becomes, can bacteria survive such a journey, given the violent heat and acceleration that would be involved in blasting them off the Earth?

Relevant work at the conference suggests that they can. As summarized by Mark Peplow in a Nature.com article, scientists at the University of Florida (Gainesville) have fired marble-sized pellets into plates containing bacterial spores in water. Their simulations find that a tiny number of bacteria survive the ordeal. That could mean that a place whose surface is not utterly inimical to life, such as Titan, could find itself hosting Earth-based life forms, provided the few bacteria that made the journey could adapt to temperatures of -170 degrees Celsius. Whether this is possible remains for future work to determine.

Centauri Dreams‘ take: I love this quote in the Nature.com story from Jeff Moore, a planetary scientist at NASA’s Ames Research Center: “Once one planet comes down with life, they all get it.” An abstract of Gladman, Dones, Levision et al., “Meteoroid Transfer to Europa and Titan,” is available here (PDF warning). And note: the abstract confusingly refers to Triton rather than Titan at one point, but the figure in question is clearly meant to depict impacts on the latter moon.

I’ve wondered if a similar process could seed life across interstellar distances. The chance of hitting a planet directly may be too low, but I wonder if spore-bearing meteoroids could be slowed and captured in the gas of a young stellar system, then possibly accrete onto a small comet or asteroid, and finally collide with a planet before radiation can sterilize them. The nebula around a young star is a much, much larger target than a planet, so the rate here might be interestingly large.

Exactly so, and I don’t find the idea at all unlikely. Which would make the spread of life, given cosmological time-scales, almost a certainty. My guess is that the real question will be not so much how far has life spread, but how widespread is sentient life, and on that issue we have all too little data!

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In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last seven years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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